Aqueous silver I selenide complexes

In the measurements performed by Mehra and Gubeli [70MEH/GUB], the solubility measurements conducted with radioactively labelled silver showed a constant dissolved silver selenide concentration of about 6 x 10 to 8 x 10 M at pH 10. The solubility was independent of the total Se(- 11) concentration in the test solutions. From this finding it was concluded that a species of the formula Ag2(HSe)(OH)(aq) was formed and its stability constant was evaluated from the data. The composition of this complex is formally equivalent to the composition Ag2Se(aq) and therefore not unique. The observed constant solubility would then correspond to an intrinsic solubility of Ag2Se(s) 

However, an alternative explanation to the minute solubility registered might be the presence of Ag2 e(s) particles of colloidal size, since only a sintered glass filter was used to separate the aqueous phase from the suspension. Therefore, this review does not accept the proposed species and the equilibrium constant presented, although perhaps a more random solubility would be expected from a faulty experimental technique. Obviously further investigations are needed in this area with a better separation technique, cf. [95RA1/FEL3]. 

At pH values well above 11, the data show an increase in the Ag(l) concentration with pH and [Se(- ll)],of The formation of the species Ag(Se)2(OH) was suggested. The stoichiometry of this species is unlikely, since Ag(l) is well known to prefer a linear co-ordination. Moreover, the derivation of its stoichiometry assumed that Se predominates in the experimental pH range, which is not correct. The composition of the complex and its formation constant are thus refuted, although soluble Ag(l)-species 

---